Choosing Engineered Beams

Use manufactured timbers to handle heavy loads and long spans

There aren't many residential job sites today that don't incorporate some form of engineered lumber, a class that includes everything from plywood and OSB sheathing to trusses and I-joists. Because of the predictable spanning and load-bearing capabilities of engineered wood beams, builders, designers, architects, and engineers have made them a common framing component in buildings with wide open spaces and big daylight openings.

Defects, like knots and voids, are never more than one layer deep in laminated veneer and glulam lumber, effectively canceling them out. Predictable performance values make it a simple matter for manufacturers to publish load tables and sizing charts, available at the lumberyard, and to offer design software on their Web sites. In addition, most lumberyards offer a beam-sizing service at little or no charge to the buyer.

Engineered lumber is uniform, reliable, and available in continuous lengths (up to 80 feet in some cases) and is manufactured to a low, 7% to 8% moisture content, so frame settling due to shrinkage is minimized.

An environmentally pleasing aspect of all engineered beam types is that they are made from renewable, second-growth timber, yet far surpass solid lumber in their performance characteristics. An engineered header above an overhead garage door opening is almost a given nowadays, but did you ever wonder why one type of beam is specced instead of another? Does the lumberyard recommend a Parallam because it's the most expensive option, the most effective, or simply because it's what they carry? The bottom line is that, given a choice between several possible options, there's no single answer. Unless you're prepared to cross-compare solid-sawn, multiple 2-bys, doubled LVL, thick LVL, glulam, PSL, and steel for best value and performance each and every time you need a girder, you'll probably continue to rely on your personal preference, your engineer's specification, or your retailer's recommendation.

Framing grade and architectural grade (shown) differ only in their appearance; there's no difference in their fabrication or strength.

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Laminated Veneer Lumber

Laminated veneer lumber (LVL), less commonly called structural composite lumber (SCL), is made from lower-grade Doug fir, southern pine, or aspen veneers taken from the outer layers of the logs. LVL is similar in appearance to plywood but, unlike cross-laminated plywood, its plies are all oriented parallel to one another. The plies are bonded with exterior exposure adhesives into a 1 3/4-inch-thick billet, then cut into standard widths from 7 1/4 to 18 inches. When ganged in multiples of two or more members, LVLs become ideal medium-span (14- to 16-foot) structural beams. Longer spans are certainly possible, using deeper beams, but not every ceiling height can accommodate a 24-inch-deep girder.

Because a built-up beam can be assembled on site, one piece at a time, LVL is often the material of choice for builders with limited manpower or on sites with restricted crane access. An LVL beam also comes in particularly handy when an opening is modified to accept a wider door or window where the existing ceiling height may restrict the header's depth.

Hammer time. On the downside, some builders curse LVLs as their guns fail to sink the nails home, common spikes bend, and arms ache from endless pounding. This puzzles Gary Dunn, an engineer at Boise Cascade, in Oregon, who claims that the laminating process increases lumber density less than 5% and that the glue lines are too thin to pose any problem. Dunn speculates that nailing problems are specific to LVLs made from southern pine, a denser species than Doug fir; he hasn't observed unusual difficulty in nailing Versa-Lam beams made from Doug fir. (Because of the way lumber veneer is produced and distributed nationally, builders east of the Mississippi have to cope with the idiosyncrasies of southern pine, unless they special-order Doug fir stock from the West.) Trus Joist 's beam and header product manager John Grogan has heard only a few comments about the nailability of Eastern Microllam, which is made from southern pine (Western Microllam is made from Doug fir). "We run our own nail testing here and haven't encountered any problems. It may be a matter of turning up the pressure on the guns." In fact, he says, "Trus Joist receives few complaints." On the other hand, Joe Madera, engineered wood specialist at Shepley Wood Products in Hyannis, Mass., has heard this complaint "a lot."

If you do have trouble gun-nailing, you can safely predrill and nail by hand, as long as you use a drill bit of smaller diameter than the nail shank. Madera steers his customers to Simpson Strong-Tie’s SDS, or Strong Drive Screw, specifically designed to stitch LVL combos together. Certain applications — for instance, when sideloading may pull laterally on the beam — call for LVLs to be lag-bolted or through-bolted together. Triple and quadruple laminations may require nails and bolts combined. Whatever method you use, it’s important to follow the manufacturer’s published fastener schedule, typically two or three rows of 3 1/4-inch nails spaced every 12 inches, to ensure proper beam performance. Many building inspectors will fail a beam if the fastener schedule isn’t strictly adhered to. Thicker, 3 1/2-inch LVL is also available to reduce the need to laminate members.

Cupping can also be a problem with LVL beams. Even through-bolting cupped beams in opposition often fails to flatten them, leaving a protruding bulge in the framing. Cupping isn't a direct result of the manufacturing process; it happens because of moisture absorption. The extreme dryness (7% to 8% moisture content) of LVLs makes them particularly susceptible to moisture uptake. They should be protected by a shelter or wrapping during storage, and, according to Madera, that is not always sufficient to prevent cupping, even after installation. "It's a big problem with this material. We have builders returning LVLs, and I don't blame them. In some cases, the stuff is so bad, it won't even fit in the hanger," he notes. Manufacturers concede the problem to some extent but claim that most cupping can be reversed by flipping the beam over in the sunshine and allowing it to equalize. Madera says that this works on returned stock about 20 percent of the time; the rest of the returns go out as scrap and dunnage.

"Cupping is really only a problem with LVL made from southern pine," says John Grogan. "We apply a protective facing that we call Watershed Overlay to our LVLs. Basically, it's a resin-impregnated paper that keeps the wood dry. The resin is activated by heat and pressure and forms an excellent bond with the Microllam in the press. We also apply a sealer to the lumber's edges." Cover up. It's a good idea to check out the storage and stock conditions in advance of purchase to avoid problems and delays. When you take delivery, pay attention to your own storage methods, too, if the beam isn't immediately installed. Keep LVL stock off the ground and wrapped in a waterproof cover. Once installed, get the roof dried-in quickly. If you allow an LVL ridge beam, for example, to hang up there in the rain and get soaked, it may soften and sag.

Glulam

While LVL beams are relative newcomers, glulams have been around for more than a generation. The first structural glued laminated timber members in America are said to be roof supports in the Peshtigo (Wisconsin) High School gymnasium, built in 1934. Great, boomerang-shaped architectural beams that soar from wall support to rafter in one continuous sweep are a common sight today in churches, gyms, and commercial buildings. They also appear in many residential projects, particularly as architectural elements. In fact, if you have a tricky curved wall or an arch to frame, a glulam could be the easiest, and possibly the least expensive, solution.

Glulam beams are typically made of either solid Douglas fir or southern pine, although other lumber species are also used, including Alaska cedar, California redwood, larch, hem-fir, Ponderosa pine, spruce-pine-fir, western red cedar, and some miscellaneous hardwoods, including oak, red oak, red maple, and yellow poplar.

Stack and glue. To manufacture a glulam, 2-by dimensional lumber is kiln-dried to about 15% moisture content, stacked, glued, and trimmed to form beams in practical depths of up to 72 inches and 60 feet long, although much larger beams have been produced for commercial applications. Pound for pound, a standard glulam beam weighs about the same as a comparably sized LVL. Generally, however, glulams are not quite as strong as LVLs of the same size. There are a couple of exceptions: Anthony Forest Products's Power Beam and Rosboro's Big Beam are made from machine-stress-rated lumber, with the strongest-rated pieces located at the outer edges. These proprietary glulams can be substituted for an LVL or Parallam of the same size.

In some cases, LVL, which is widely available, might be overkill. According to at least one glulam manufacturer, swapping in a glulam beam could save you up to 10 percent in material cost over an LVL or PSL beam. (In some markets, though, glulams are the higher-cost alternative.)

Surface dressing. Industry standards for glulams include "architectural" and "framing" beams, which differ only in appearance (the architectural grade has its minor defects filled and its surface cleaned up); they are the same in composition and performance.

Glulam beams are manufactured with and without built-in camber, which means that your glulam may have specific "up" and "down" edges.

Exposure. Glulams are susceptible to warping if improperly stored. Use a flat surface and block the beam to prevent it from sagging and taking a set. Store long beams on edge. Like LVL, this lumber is extremely dry, so protection from moisture is critical, because surface and end checking from moisture absorption reduces the strength of the beam. Manufacturers usually apply a penetrating sealer to all surfaces before shipment — Rosboro calls its product Liquid Wrap — and individual beams are normally delivered to the site in a protective wrapper. Also, watch out for excessive exposure to sunlight, which will give the beams a tired, gray, used look. To protect the beam from damage, soiling, sun, and moisture, it's best to leave the wrapper in place until the building is dried-in. For long-term outdoor exposure, such as for deck construction or ground-contact applications, glulams can be ordered in pressure-treated southern pine.